Field of the Invention
The present invention relates to a depth detection apparatus, an imaging apparatus, and a depth detection method.
Description of the Related Art
As a depth detection technique that can be applied to a digital camera, a depth detection technique providing a depth measuring function to a part or all of the pixels of image pickup elements, and detecting the depth to an object based on the phase contrast method, is known. The pixel having a depth measuring function (hereafter called “depth measuring pixel”) has a plurality of photoelectric conversion units which receive luminous flux that passed through different regions on a pupil of the imaging optical system respectively. The shift amount of an image signal generated by each photoelectric conversion unit is estimated, and the depth is measured by converting the shift amount into a defocus amount using a conversion coefficient.
One factor that drops the depth measuring accuracy is a change in the profile of the image signal generated by each photoelectric conversion unit. If the image signal generated by each photoelectric conversion unit has a different profile from each other, due to the eclipse of luminous flux caused by a frame of the optical system or the like, and has a difference in sensitivity characteristic among the pixels, the accuracy to estimate the shift amount of the image signal drops, and the depth measuring accuracy drops accordingly.
Japanese Patent No. 5606208 discloses a method for correcting the profile difference by filtering the image signals so as to improve the shift amount detection accuracy. The profile difference among the image signals changes in accordance with the defocus amount. Therefore according to Japanese Patent No. 5606208, the shift amount is provisionally calculated using the image signal before correction (hereafter called “provisional image shift amount”), whereby an approximate value of the defocus amount is detected, and the image profile is corrected using a filter generated based on this result.
Patent Document 1: Japanese Patent No. 5606208